The invention relates to an electric furnace, such as an electric arc furnace or a plasma melting furnace, with a lifting means actuating the furnace cover and comprising a king post supported on a base and a sleeve surrounding the king post and being liftable and lowerable relative to the same and provided with a cap on its upper end, which sleeve is hydraulically liftable and engageable with a cover carrying structure carrying the furnace cover.
With known furnaces of this kind a hydraulic cylinder piston unit acting only in the lifting direction is installed between a front-side recess of the king post and the bottom of the sleeve.
Articulation bearings are installed between the king post and the sleeve, which are fastened to the sleeve and are moved with the same.
The recess provided in the king post for the cylinder piston unit necessitates a larger diameter of the king post and thus of the sleeve, the known structure thus having a considerable weight.
Due to the double guidance of the sleeve at the king post, i.e., by means of the articulation bearings on the one hand and by means of the hydraulic cylinder-piston unit on the other hand, constraining forces occur, which delimit the functionability of the structure and also cause an increased wear. Jamming of the sleeve on the king post might occur, possibly causing difficulties to arise during lowering, namely when the load support provided on the sleeve for the cover supporting structure gets jammed on the same and the weight of the sleeve does not suffice for counteracting these jamming forces and the constraining forces resulting from the double guidance thus impeding the lowering movement. In this case the furnace has to be set out of operation.